Method of applying force to electrical contacts on a printed circuit board

ABSTRACT

A spring actuated clamping mechanism has a backer plate with an upper surface and a lower surface. A set of apertures is formed along the periphery of the backer plate. The upper surface of the backer plate has at least one backer plate recess, and preferably four recesses, formed therein. A threaded aperture is also formed in the backer plate. A compression plate is also provided. A second set of apertures is formed along the periphery of the compression plate. The lower surface of the compression plate has at least one compression plate recess, and at least one compression plate aperture. At least one compression spring is disposed between the backer plate and the compression plate. A screw tension release mechanism is screwed into the backer plate threaded aperture and inserted through the compression plate aperture. When the release mechanism is loosened, backer plate is forced downwardly, applying a uniform force to all electrical contacts on the printed circuit board or card to which the clamping mechanism is attached.

RELATED APPLICATIONS

The present application is a divisional application of application Ser.No. 12/215,079, which is incorporated by reference herein in itsentirety.

FIELD OF THE INVENTION

The present invention relates to clamping mechanisms for the applicationof force to electrical contacts in printed circuit boards (PCBs) and,more particularly, to a spring actuated clamping mechanism for applyinguniform force to PCB electrical contacts.

BACKGROUND OF THE INVENTION

Pressure or force is a necessary evil in most electronic packages. Inorder for an electrical circuit to be made, mechanical connectionsbetween electric terminals or contacts is required. In general, ofcourse, the higher the number of electrical connection to be made, thegreater the force that is needed. In the case of delicate land gridarray (LGA) printed circuit cards and boards having hundreds orthousands of electrical contacts, however, great contacting force can becounterproductive. That is, small and delicate pads, lands, and contactsmust withstand appreciable forces applied thereto. The present state ofthe art packages produced by the Assignee of the present inventioninclude 5,448 contacts, each of which requires 60 g. of force to ensurea proper reliable electrical connection.

Another problem with applying forces to electrical contacts, especiallyaround the periphery of a LGA connector, is the unequal application andmismatch of such force, sometimes resulting in skewing of thecomponents. This results in better connections along a certain portionof the bank of contacts than along another portion thereof.

DISCUSSION OF RELATED ART

U.S. Pat. No. 6,477,058 for INTEGRATED CIRCUIT PACKAGE DEVICE INCLUDINGMULTIPLE STACKED COMPONENTS, issued Nov. 5, 2002 to Richard J. Luebs etal teaches an integrated circuit device package comprising a LGAinterposer socket positioned between, and in communication with, an LGAintegrated circuit device and a first side of a first circuit board; asecond LGA interposer socket positioned between, and in communicationwith, a second circuit board and a second side of the first circuitboard, wherein the second side of the first circuit board is opposite toand parallel with the first side of the first circuit board; and aclamping mechanism for compressively urging together the LGA integratedcircuit device, the first LGA interposer socket, the first circuitboard, the second LGA interposer socket, and the second circuit boardinto electrical interconnection under a predetermined load.

U.S. Pat. No. 6,549,418 for LAND GRID ARRAY INTEGRATED CIRCUIT DEVICEMODULE, issued Apr. 15, 2003 to Jeffrey L. Deeney teaches an integratedcircuit device module comprising a printed circuit board having opposedsides, the printed circuit board comprising a portion carrying an areacontact array on one of the sides of the printed circuit board. Themodule comprises an integrated circuit device having opposed, top andbottom surfaces, the bottom surface of the integrated circuit devicecomprising an area contact array for electrical communication with thearea contact array on the printed circuit board. The module furthercomprises a clamping mechanism for compressively urging the area contactarray on the bottom surface of the integrated circuit device intoelectrical communication with the area contact array on the portion ofthe printed circuit board. A biasing structure is coupled to the printedcircuit board for counteracting the forces applied by the clampingmechanism and the resulting tendency of the portion of the printedcircuit board to deflect.

It would be advantageous to provide apparatus for applying pressure orforce to electrical contacts.

It would also be advantageous to apply pressure to electrical contactsin an LGA uniformly.

It would also be advantageous to apply pressure to all electricalcontacts simultaneously.

It would further be advantageous to prevent damage to electricalcontacts upon the application of pressure thereto.

It would still further be advantageous to apply pressure by means of apreloaded device.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a springactuated clamping mechanism. A backer plate has a set of aperturesformed along the periphery. The upper surface of the backer plate has atleast one backer plate recess, and preferably four recesses, formedtherein. A threaded aperture is also formed in the backer plate. Acompression plate is provided with a second set of apertures formedalong the periphery of the compression plate, each of the set ofcompression plate apertures corresponding to each of the set of backerplate apertures. The lower surface of the compression plate has at leastone compression plate recess, and at least one compression plateaperture. At least one compression spring, and preferably four springs,is disposed between the backer plate and the compression plate. Thecompression spring(s) is retained by the respective backer plate andcompression plate recesses. A screw tension release mechanism is screwedinto the backer plate aperture and inserted through the compressionplate aperture.

BRIEF DESCRIPTION OF THE DRAWINGS

A complete understanding of the present invention may be obtained byreference to the accompanying drawings, when considered in conjunctionwith the subsequent detailed description, in which:

FIG. 1 is a perspective view of the clamping mechanism in accordancewith the present invention;

FIG. 2 is a side view of the clamping mechanism showing compressionsprings;

FIGS. 3 a and 3 b are plan views of the lower surface of compressionplate and the upper surface of backer plate, respectively;

FIG. 3 c is a plan view of the upper surface of backer plate withcompression springs disposed thereon;

FIG. 4 is a plan view of the lower surface of backer plate; and

FIG. 5 is a side, in situ view of the spring actuated clamping mechanismof the present invention.

For the sake of clarity and brevity, like elements and components ofeach embodiment will bear the same designations throughout thedescription.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Generally speaking, the present invention features a spring actuatedclamping mechanism that has a backer plate. A set of apertures isdrilled or otherwise formed along the periphery of the backer plate. Acompression plate having an aperture is also provided. At least onecompression spring is disposed between the backer plate and thecompression plate. A release mechanism is screwed into the backer plateaperture and inserted through the compression plate aperture.

Referring now to FIG. 1, there is shown a perspective view of the springactuated clamping mechanism 10 in accordance with the invention.Clamping mechanism 10 has a substantially planar, rectangular backerplate 12. Backer plate 12 is steel and has eight spaced apart apertures14 formed around the periphery thereof.

A steel compression plate 16, having similar or identical dimensions tobacker plate 12, also has a plurality of spaced apart apertures 18around the periphery thereof. A set of compression springs (not shown inthis figure), described in greater detail hereinbelow, separates backerplate 12 from compression plate 16. Any number of compression springscan be used, depending upon the configuration of the respective plates12, 16. Preferably, however, an even number of compression springs isincorporated in the clamping mechanism 10.

At or about the center of compression plate 16 is a central compressionaperture 22 (FIG. 3 a) that is aligned with a central backer aperture,not shown in this figure, in backer plate 12. Threaded through centralapertures 22, 24 is a screw tension release rod 26, the upper portion ofwhich is retained by a washer and nut 28, 39, respectively. Nut 30 canbe tightened to clamp backing plate 12 and compression plate 16 and totighten, and therefore displace, compression springs 20 (FIG. 2). Ashoulder 31 is also provided on release rod 26 to limit the appliedforce so as not to over-compress compression springs 20.

Referring now to FIGS. 2, 3 a, 3 b and 3 c there is shown a cutaway viewof clamping mechanism 10. Each compression spring 20 is seated in arecess 32 on the upper surface 12 a of backer plate 12 and in thecorresponding recess 34 on the lower surface of compression plate 16 b.

Referring now to FIG. 4 there is shown the clamping mechanism 10 fromthe lower surface 12 b of backer plate 12. Centrally located aperture 24securely retains the lower plate 28 of rod 26 (FIG. 3 c). In otherwords, rod 26 is permanently attached to backer plate 12 via aperture24.

Referring now to FIG. 5 there is shown a cross-sectional view of theclamping mechanism 10 positioned via eight alignment posts 30 throughback plate apertures 18 and compression plate aperture 16 to a heatspreader or heat sink 32 having an IC device or module 34 attachedthereto. A PC board 36 having one or more connectors 38 mounted thereonis positioned relative to the IC device 34 on the lower surface of PCboard 36 can be mounted an insulator 40.

In operation, each of the periphery apertures 14, 18 receives analignment post 30 that is connected to heat sink 32 on printed circuitboard or card 36, not shown, for which pressure is required. Clampingmechanism 10 is first pre-tensioned by tightening nut 39 and placingclamping mechanism 10 over the subject printed circuit board or card 36by means of posts 30 connected to heat sink 32 on or proximate circuitboard or card 36. An insulator plate, not shown, used to prevent anyelectrical short that can occur if the metal backer plate 12 contactsthe pads on the printed circuit board or card 36. Once appropriatelypositioned, nuts and washers are used to hold clamping mechanism 10against the board or card 36. The clamping mechanism 10 is used to applypressure uniformly to all electrical contacts 34, 38 proximate the lowersurface 12 b of backer plate 12. Activation of the clamping mechanism 10is accomplished by unscrewing nut 39 so that compression springs 20 arepermitted to expand and force backer plate 12 against board 36 and ICmodule 34. At this point, nut 39 and corresponding washer can be removedfrom clamping mechanism 10.

Since other modifications and changes varied to fit particular operatingrequirements and environments will be apparent to those skilled in theart, the invention is not considered limited to the examples chosen forpurposes of disclosure, and covers all changes and modifications whichdo not constitute departures from the true spirit and scope of thisinvention.

Having thus described the invention, what is desired to be protected byLetters Patent is presented in the subsequently appended claims.

1. A method of applying force to electrical contacts on a printedcircuit board, the steps comprising: a) providing a backing plate with aplurality of apertures around the periphery thereof, at least onecenter, threaded aperture, and at least one recess in the upper surfacethereof; b) placing at least one compression spring in said backingplate recess; c) fastening a screw tension release rod into said atleast one threaded aperture, said screw tension release rod having asuitably sized nut; d) providing a compression plate having a pluralityof apertures around the periphery thereof and a center aperture formedtherein; e) aligning said compression plate over said at least onecompression spring and over said backer plate, said compression platebeing aligned over said backer plate so as to align said backer plateapertures with said compression plate apertures; f) inserting said screwtension release rod into said compression plate center aperture; g)screwing a nut onto said screw tension release rod to clamp saidcompression plate and said backer plate together, creating a clampingassembly; h) using posts inserted into said backer plate apertures andsaid compression plate apertures to attach said clamping assembly to aprinted circuit board having electrical contacts, said attaching step(h) comprising tightening nuts screwed to said screw tension releaserod; and i) releasing said center nut to activate said clampingassembly.
 2. The method of applying force to electrical contacts on aprinted circuit board in accordance with claim 1, wherein said lowersurface of said backer plate is configured in one of the group: planarand convex.
 3. The method of applying force to electrical contacts on aprinted circuit board in accordance with claim 1, wherein said at leastone backer plate recess and said at least one compression plate recesscomprises four recesses, respectively.
 4. The method of applying forceto electrical contacts on a printed circuit board in accordance withclaim 3, wherein said at least one compression spring comprises fourcompression springs, each corresponding to one of said four compressionplate recesses.
 5. The method of applying force to electrical contactson a printed circuit board in accordance with claim 4, wherein said atleast one compression spring comprises four compression springs, eachcorresponding to one of said four backer plate recesses.
 6. The methodof applying force to electrical contacts on a printed circuit board inaccordance with claim 1, wherein said threaded backer plate aperturecorresponds to and is aligned with said compression plate aperture. 7.The method of applying force to electrical contacts on a printed circuitboard in accordance with claim 6, further comprising a nut disposedproximate said upper surface of said compression plate and saidcompression aperture for retaining said screw tension release mechanismtherein.